Hydrodynamical simulations of planet rebound migration in photo-evaporating disks

¹ Institute for Astronomy, School of Physics, Zhejiang University, Hangzhou 310027, China
² Center for Cosmology and Computational Astrophysics, Institute for Advanced Study in Physics, Zhejiang University, Hangzhou 310027, China
³ IRAP, Université de Toulouse, CNRS, CNES, Toulouse, France
⁴ Department of Physics and Astronomy, University of Nevada, Las Vegas, NV 89154-4002, USA
⁵ Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030, China
⁶ TU Delft, Faculty of Aerospace Engineering, Kluyverweg 1, 2629 HS Delft, The Netherlands

^★ Corresponding author: bbliu@zju.edu.cn

Received: 30 June 2025
Accepted: 5 September 2025

Abstract

This study investigates the orbital migration of a planet located near the truncated edge of protoplanetary disks, induced by X-ray photo-evaporation originating from the central star. The combined effects of turbulent viscous accretion and stellar X-ray photo-evaporation give rise to the formation of a cavity in the central few astronomical units in disks. Once the cavity is formed, the outer disk experiences rapid mass loss and the cavity expands from the inside out. We conducted 2D hydrodynamical simulations of planet-disk interaction for various planet masses and disk properties. Our simulations demonstrate that planets up to about Neptune masses experience a strong positive corotation torque along the cavity edge that leads to sustained outward migration – a phenomenon previously termed rebound migration. Rebound migration is more favorable in disks with moderate stellar photo-evaporation rates of ~10⁻⁸ M_⊙ yr⁻¹. Saturn-mass planets only experience inward migration, due to significant gas depletion in their co-orbital regions. In contrast, Jupiter-mass planets are found to undergo modest outward migration as they cause the residual disk to become eccentric. This work presents the first 2D hydrodynamical simulations that confirm the existence and viability of rebound outward migration during the inside-out clearing in protoplanetary disks.